U.S. patent application number 11/689642 was filed with the patent office on 2007-10-18 for magnetic material for magnetic refrigeration.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Tadahiko Kobayashi, Akiko Saito, Shinya Sakurada, Hideyuki Tsuji.
Application Number | 20070241305 11/689642 |
Document ID | / |
Family ID | 38603979 |
Filed Date | 2007-10-18 |
United States Patent
Application |
20070241305 |
Kind Code |
A1 |
Sakurada; Shinya ; et
al. |
October 18, 2007 |
MAGNETIC MATERIAL FOR MAGNETIC REFRIGERATION
Abstract
A magnetic material for magnetic refrigeration has a composition
represented by (R1.sub.1-yR2.sub.y).sub.xFe.sub.100-x (R1 is at
least one of element selected from Sm and Er, R2 is at least one of
element selected from Ce, Pr, Nd, Tb and Dy, and x and y are
numerical values satisfying 4.ltoreq.x.ltoreq.20 atomic % and
0.05.ltoreq.y.ltoreq.0.95), and includes a Th.sub.2Zn.sub.17
crystal phase, a Th.sub.2Ni.sub.17 crystal phase, or a TbCu.sub.7
crystal phase as a main phase.
Inventors: |
Sakurada; Shinya; (Tokyo,
JP) ; Saito; Akiko; (Kawasaki-shi, JP) ;
Kobayashi; Tadahiko; (Yokohama-shi, JP) ; Tsuji;
Hideyuki; (Yokohama-shi, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
38603979 |
Appl. No.: |
11/689642 |
Filed: |
March 22, 2007 |
Current U.S.
Class: |
252/62.57 ;
148/105; 252/62.63; 75/244 |
Current CPC
Class: |
C22C 38/005 20130101;
H01F 1/015 20130101; C22C 45/02 20130101; F25B 21/00 20130101 |
Class at
Publication: |
252/062.57 ;
252/062.63; 075/244; 148/105 |
International
Class: |
C04B 35/40 20060101
C04B035/40; C04B 35/26 20060101 C04B035/26; H01F 1/03 20060101
H01F001/03; C22C 29/14 20060101 C22C029/14 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 2006 |
JP |
2006-086421 |
Claims
1. A magnetic material for magnetic refrigeration, comprising: a
composition represented by a general formula:
(R1.sub.1-yR2.sub.y).sub.xFe.sub.100-x where, R1 is at least one of
element selected from Sm and Er, R2 is at least one of element
selected from Ce, Pr, Nd, Tb and Dy, x is a value satisfying
4.ltoreq.x.ltoreq.20 atomic % and y is a value satisfying
0.05.ltoreq.y.ltoreq.0.95, wherein the magnetic material includes a
Th.sub.2Zn.sub.17 crystal phase, a Th.sub.2Ni.sub.17 crystal phase
or a TbCu.sub.7 crystal phase as a main phase.
2. The material according to claim 1, wherein the magnetic material
exhibits a second order magnetic phase transition.
3. The material according to claim 1, wherein the magnetic material
has a Curie temperature of 320K or less.
4. The material according to claim 1, wherein the element R2
contains 70 atomic % or more of at least one selected from Ce, Pr
and Nd of.
5. The material according to claim 1, wherein the element R2 is
composed of at least one selected from Ce, Pr and Nd.
6. The material according to claim 1, wherein a part of the element
R2 is replaced by at least one of element selected from La, Gd, Ho,
Y, Tm and Yb.
7. The material according to claim 1, wherein a part of the Fe is
replaced by at least one of element selected from Ti, V, Cr, Mn,
Co, Ni, Cu, Zn, Zr, Nb, Mo, Hf, Ta, W, Al, Si, Ga and Ge.
8. The material according to claim 1, wherein a part of the Fe is
replaced by at least one of element selected from Ni, Co, Mn, Ti,
Zr, Al and Si.
9. The material according to claim 1, wherein the magnetic material
includes the Th.sub.2Zn.sub.17 crystal phase or the
Th.sub.2Ni.sub.17 crystal phase as the main phase.
10. The material according to claim 1, wherein the magnetic
material includes the Th.sub.2Zn.sub.17 crystal phase as the main
phase.
11. A magnetic material for magnetic refrigeration, comprising: a
composition represented by a general formula:
(R.sub.1-yX.sub.y).sub.xFe.sub.100-x where, R is at least one of
element selected from La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm,
Yb and Y, X is at least one of element selected from Ti, Zr and Hf,
x is a value satisfying 4.ltoreq.x.ltoreq.20 atomic % and y is a
value satisfying 0.01.ltoreq.y.ltoreq.0.9, wherein the magnetic
material includes a Th.sub.2Ni.sub.17 crystal phase or a TbCu.sub.7
crystal phase as a main phase.
12. The material according to claim 11, wherein the magnetic
material exhibits a second order magnetic phase transition.
13. The material according to claim 11, wherein the magnetic
material has a Curie temperature of 320K or less.
14. The material according to claim 11, wherein the element R
contains 50 atomic % or more of at least one selected from Ce, Pr,
Nd and Sm.
15. The material according to claim 11, wherein the element R is
composed of at least one selected from Ce, Pr, Nd and Sm.
16. The material according to claim 11, wherein the value y is in a
range from 0.01 to 0.5.
17. The material according to claim 11, wherein a part of the Fe is
replaced by at least one of element selected from V, Cr, Mn, Co,
Ni, Cu, Zn, Nb, Mo, Ta, W, Al, Si, Ga and Ge.
18. The material according to claim 11, wherein a part of the Fe is
replaced by at least one of element selected from Ni, Co, Mn, Cr,
V, Nb, Mo, Al, Si and Ga.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No. 2006-086421
filed on Mar. 27, 2006; the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a magnetic material used
for magnetic refrigeration.
[0004] 2. Description of the Related Art
[0005] Most of refrigeration technologies for use in a room
temperature region such as refrigerators, freezers, and
air-conditioners use a gas compression cycle. But, the
refrigeration technologies based on the gas compression cycle have
a problem of causing environmental destruction associated with the
exhaustion of specific freon gases to the environment, and there is
also concern that substitute freon gases have an adverse effect
upon the environment. Under the circumstances described above,
clean and highly efficient refrigeration technologies, which are
free from environmental problems caused by wastage of operating
gases, have been demanded to be put into practical use.
[0006] Recently, magnetic refrigeration is being increasingly
expected as one of such environment-friendly, highly efficient
refrigeration technologies. Research and development of magnetic
refrigeration technologies for use in a room temperature region is
underway. The magnetic refrigeration technologies use the
magnetocaloric effect of magnetic material instead of freon gases
or substitute freon gases as a refrigerant to realize a
refrigeration cycle. Specifically, the refrigeration cycle is
realized by using a magnetic entropy change (.DELTA.S) of the
magnetic material associated with a magnetic phase transition
(phase transition between a paramagnetic state and a ferromagnetic
state). In order to realize the highly efficient magnetic
refrigeration, it is preferable to use a magnetic material which
exhibits a high magnetocaloric effect around room temperature.
[0007] As such a magnetic material, a single rare earth element
such as Gd, a rare earth alloy such as Gd--Y alloy or Gd-Dy alloy,
Gd.sub.5(Ge, Si).sub.4 based material, La(Fe, Si).sub.13 based
material, Mn--As--Sb based material and the like are known (JP-A
2002-356748 (KOKAI) and JP-A 2003-096547 (KOKAI)). The magnetic
phase transition of the magnetic material is in two types including
a first order type and a second order type. The Gd.sub.5(Ge,
Si).sub.4 based material, the La(Fe, Si).sub.13 based material and
the Mn--As--Sb based material exhibit the first order magnetic
phase transition. These magnetic materials can be used to easily
obtain a large entropy change (.DELTA.S) by the application of a
low magnetic field but has a practical problem that its operating
temperature range is narrow.
[0008] A rare earth metal such as Gd and a rare earth alloy such as
Gd--Y alloy or Gd--Dy alloy exhibit the second order magnetic phase
transition, so that they have advantages that they can operate in a
relatively wide temperature range and also have a relatively large
entropy change (.DELTA.S). But, the rare earth element itself is
expensive, and when the rare earth element or the rare earth alloy
is used as a magnetic material for magnetic refrigeration, it is
inevitable that the cost of the magnetic material for magnetic
refrigeration becomes high.
[0009] Besides, it is also known that a
(Ce.sub.1-xY.sub.x).sub.2Fe.sub.17(x=0 to 1) based magnetic
material exhibits the second order magnetic phase transition. The
(Ce, Y).sub.2Fe.sub.17 based magnetic material can operate in a
relatively wide temperature range in the same manner as the rare
earth element and the rare earth alloy, and it is a substance based
on inexpensive Fe, so that the cost of the magnetic material for
magnetic refrigeration can be made lower than the rare earth metal
or the rare earth alloy. However, the (Ce, Y).sub.2Fe.sub.17 based
magnetic material has high magnetic anisotropy, so that it has a
disadvantage that a magnetic entropy change amount (.DELTA.S)
associated with the magnetic phase transition is small.
SUMMARY OF THE INVENTION
[0010] A magnetic material for magnetic refrigeration according to
an aspect of the present invention has a composition represented by
a general formula: (R1.sub.1-yR2.sub.y).sub.xFe.sub.100-x (where,
R1 is at least one of element selected from Sm and Er, R2 is at
least one of element selected from Ce, Pr, Nd, Tb and Dy, and x and
y are numerical values satisfying 4.ltoreq.x.ltoreq.20 atomic % and
0.05.ltoreq.y.ltoreq.0.95), and includes a Th.sub.2Zn.sub.17
crystal phase, a Th.sub.2Ni.sub.17 crystal phase or a TbCu.sub.7
crystal phase as a main phase.
[0011] A magnetic material for magnetic refrigeration according to
another aspect of the present invention has a composition
represented by a general formula:
(R1.sub.1-yX.sub.y).sub.xFe.sub.100-x (where, R is at least one of
element selected from La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm,
Yb and Y, X is at least one of element selected from Ti, Zr and Hf,
and x and y are numerical values satisfying 4.ltoreq.x.ltoreq.20
atomic % and 0.01.ltoreq.y.ltoreq.0.9), and includes a
Th.sub.2Ni.sub.17 crystal phase or a TbCu.sub.7 crystal phase as a
main phase.
BRIEF DESCRIPTION OF THE DRAWING
[0012] FIG. 1 is a diagram showing Curie temperatures in R--Fe
based materials and 4f electron orbits of rare earth elements
R.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Hereinafter, embodiments of the present invention are
described. A magnetic material for magnetic refrigeration according
to a first embodiment has a composition expressed by the following
general formula: (R1.sub.1-yR2.sub.y).sub.xFe.sub.100-x (1) (where,
R1 is at least one of element selected from Sm and Er, R2 is at
least one of element selected from Ce, Pr, Nd, Tb and Dy, and x and
y are numerical values satisfying 4.ltoreq.x.ltoreq.20 atomic % and
0.05.ltoreq.y.ltoreq.0.95), and includes a Th.sub.2Zn.sub.17
crystal phase, a Th.sub.2Ni.sub.17 crystal phase or a TbCu.sub.7
crystal phase as a main phase.
[0014] The magnetic material for magnetic refrigeration is a
material having a rare earth element (element R) and iron (Fe) as
main components and inexpensive Fe as a base. Specifically, the
second order magnetic phase transition is realized by a magnetic
material having the rare earth element in a small amount. In order
to realize the second order magnetic phase transition by such
material, the magnetic material for magnetic refrigeration has a
Th.sub.2Zn.sub.17 crystal phase (phase having a Th.sub.2Zn.sub.17
type crystal structure), a Th.sub.2Ni.sub.17 crystal phase (phase
having a Th.sub.2Ni.sub.17 type crystal structure), or a TbCu.sub.7
crystal phase (phase having a TbCu.sub.7 type crystal structure) as
a main phase. The main phase shall be a phase occupying a maximum
volume among the constituent phases (including crystal phases and
amorphous phases) of the magnetic material for magnetic
refrigeration.
[0015] The magnetic material having the Th.sub.2Zn.sub.17 crystal
phase has the element R mainly entered a position corresponding to
the Th of the Th.sub.2Zn.sub.17 crystal phase, and the Fe mainly
entered a position corresponding to the Zn of the Th.sub.2Zn.sub.17
crystal phase. Similarly, the magnetic material having the
Th.sub.2Ni.sub.17 crystal phase has the element R mainly entered a
position corresponding to the Th, and the Fe mainly entered a
position corresponding to the Ni. The magnetic material having the
TbCu.sub.7 crystal phase has the element R mainly entered a
position corresponding to the Tb, and the Fe mainly entered a
position corresponding to the Cu.
[0016] The magnetic material of the first embodiment has the rare
earth element in a small content as indicated by a site occupying
atom of each crystal phase and an atom ratio between the element R
and Fe based on it, so that the second order magnetic phase
transition is realized by an inexpensive material. To realize the
magnetic material exhibiting the second order magnetic phase
transition by using the Th.sub.2Zn.sub.17 crystal phase, the
Th.sub.2Ni.sub.17 crystal phase or the TbCu.sub.7 crystal phase as
the main phase, the value x in the formula (1) shall be in a range
from 4 to 20 atomic %. When the value x is less than 4 atomic % or
exceeds 20 atomic %, the magnetic material having the
Th.sub.2Zn.sub.17 crystal phase, the Th.sub.2Ni.sub.17 crystal
phase or the TbCu.sub.7 crystal phase as the main phase cannot be
realized. The value x is more preferably in a range from 8 to 15
atomic %.
[0017] The main phase of the magnetic material may be anyone of the
Th.sub.2Zn.sub.17 crystal phase, the Th.sub.2Ni.sub.17 crystal
phase and the TbCu.sub.7 crystal phase. By using anyone of these
crystal phases as the main phase, the magnetic material exhibiting
the second order magnetic phase transition can be realized. But,
the TbCu.sub.7 crystal phase is a high-temperature phase, and a
rapid solidification step or the like is required to stabilize it
in a normal temperature range. Meanwhile, the Th.sub.2Zn.sub.17
crystal phase and the Th.sub.2Ni.sub.17 crystal phase are stable
under normal temperature. To reduce the production cost of the
magnetic material, it is preferable that the magnetic material has
the Th.sub.2Zn.sub.17 crystal phase or the Th.sub.2Ni.sub.17
crystal phase as the main phase.
[0018] It depends on the kind of rare earth element R as shown in
FIG. 1 whether the main phase of the magnetic material becomes the
Th.sub.2Zn.sub.17 crystal phase or the Th.sub.2Ni.sub.17 crystal
phase. When the rare earth element R is Ce, Pr, Nd, Sm or the like,
it becomes the Th.sub.2Zn.sub.17 crystal phase. If the rare earth
element R is Tb, Dy, Ho, Er or the like, it becomes the
Th.sub.2Ni.sub.17 crystal phase. As described later, the element R2
is preferably at least one selected from Ce, Pr and Nd. Therefore,
it is preferable that the main phase of the magnetic material is
the Th.sub.2Zn.sub.17 crystal phase.
[0019] In a case where the magnetic material is used as a magnetic
refrigeration material, a temperature (Curie temperature)
indicating the magnetic phase transition (phase transition between
a paramagnetic state and a ferromagnetic state) and a magnitude
(.DELTA.S) of the magnetic entropy change associated with the
magnetic phase transition are significant. FIG. 1 shows a Curie
temperature of the R--Fe based material to which various kinds of
rare earth elements R are applied. As shown in FIG. 1, the
application of Ce, Pr, Nd, Sm, Tb, Dy or Er as the element R can
control the Curie temperature of the magnetic material to be close
to room temperature. When the Curie temperature is close to room
temperature, it means that the magnetocaloric effect can be
obtained near room temperature. The Curie temperature of the
magnetic material is preferably 320K or less, and more preferably
250K or more and 320K or less in view of improvement of its
usefulness as the magnetic refrigeration material. The Curie
temperature of the magnetic material is more preferably 270K or
more.
[0020] The magnetic entropy change amount (.DELTA.S) associated
with the magnetic phase transition is affected by the magnetic
anisotropy of the magnetic material. In other words, a large
magnetic entropy change amount (.DELTA.S) can be obtained by
reducing the magnetic anisotropy of the magnetic material. Here,
the individual figures (spherical, vertically long oval or
horizontally long oval) shown in FIG. 1 indicate 4f electron orbits
of the rare earth element R. For example, the 4f electron orbit of
Gd is circular, indicating that the magnetic anisotropyis small.
Therefore, the R--Fe based material to which Gd is applied as the R
element has a large magnetic entropy change amount (.DELTA.S). But,
the Gd--Fe based material is poor in usability because the Curie
temperature is excessively high.
[0021] The 4f electron orbits of Sm and Er indicate cigar like long
electron orbits, and those of Ce, Pr, Nd, Tb and Dy indicate
pancake-like flattened electron orbits. The R--Fe based material
independently using these rare earth elements R has a large
magnetic anisotropy and, therefore, a sufficient magnetic entropy
change amount (.DELTA.S) cannot be obtained. Meanwhile, where at
least one of element R1 selected from Sm and Er and at least one of
element R2 selected from Ce, Pr, Nd, Tb and Dy are used as a
mixture, the 4f electron orbit is adjusted by a long electron or
bit and a flattened electron orbit, so that the magnetic anisotropy
can be lowered.
[0022] The magnetic material having the composition expressed by
the formula (1) applies a mixture of element R1 and element R2 as
the rare earth element to lower the magnetic anisotropy. Therefore,
a magnetic material having a Curie temperature of 250K or more and
320K or less and showing a large magnetic entropy change amount
(.DELTA.S) at a relatively low magnetic field can be realized on
the basis of the element R1 and the element R2. In order to obtain
an increased effect of .DELTA.S, the value y in the formula (1) is
determined to fall in a range from 0.05 to 0.95. When the value y
is not in this range, the mixing effect of the element R1 and the
element R2 cannot be obtained satisfactorily. It is preferable that
the value y is in a range from 0.25 to 0.75 in order to obtain the
improvement effect of .DELTA.S with better reproducibility.
[0023] The element R2 may be at least one selected from Ce, Pr, Nd,
Tb and Dy. The use of at least one selected from Ce, Pr and Nd as
the element R2 enables to increase saturation magnetization of the
magnetic material. The increase in saturation magnetization of the
magnetic material for magnetic refrigeration contributes to the
increase of .DELTA.S. Therefore, the element R2 preferably contains
at least one selected from Ce, Pr and Nd in 70 atomic % or more of
a total amount of the element R2. Besides, the element R2 is more
preferably at lease one selected from Ce, Pr and Nd.
[0024] The magnetic material is not limited to the composition
expressed by the formula (1) but may have a composition which has
the element R or Fe partially replaced by another element. A part
of the element R2 may be replaced by at least one of element R3
selected from La, Gd, Ho, Y, Tm and Yb. The partial replacement of
the element R2 by the element R3 enables to control the magnetic
anisotropy of the magnetic material and the Curie temperature. But,
if the replacement amount by the element R3 is excessively large,
the magnetic entropy change might be lowered conversely. Therefore,
it is preferable that the replacement amount by the element R3 is
20 atomic % or less of the element R2.
[0025] A part of Fe may be replaced by at least one of element M1
selected from Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Nb, Mo, Hf, Ta, W,
Al, Si, Ga and Ge. By partially replacing Fe by the element M1, the
magnetic anisotropy can be further lowered or the Curie temperature
can be controlled. The element M1 is more preferably at least one
selected from Ni, Co, Mn, Ti, Zr, Al and Si. But, if the
replacement amount by the element M1 is excessively large,
magnetization is deteriorated, and the magnetic entropy change is
possibly lowered. Therefore, the replacement amount by the element
M1 is preferably 20 atomic % or less of Fe.
[0026] The magnetic material for magnetic refrigeration of the
first embodiment includes a composition having the rare earth
element R in a small amount, exhibiting a second order magnetic
phase transition, having a Curie temperature near room temperature
(e.g., 320K or less), and exhibiting a large magnetic entropy
change (.DELTA.S) at a relatively low magnetic field. Therefore, a
magnetic material for magnetic refrigeration having high
performance and excelling in practical utility can be provided at a
low cost. Such a magnetic material for magnetic refrigeration is
applied to a heat regenerator, a magnetic refrigeration device and
the like. At that time, it can also be used in combination with,
for example, the magnetic material exhibiting a first order
magnetic phase transition.
[0027] The magnetic material for magnetic refrigeration according
to a second embodiment of the invention will be described. The
magnetic material for magnetic refrigeration of the second
embodiment has a composition expressed by the following general
formula: (R.sub.1-yX.sub.y).sub.xFe.sub.100-x (2) (where, R is at
least one of element selected from La, Ce, Pr, Nd, Sm, Gd, Tb, Dy,
Ho, Er, Tm, Yb and Y, X is at least one of element selected from
Ti, Zr and Hf, and x and y are numerical values satisfying
4.ltoreq.x.ltoreq.20 atomic % and 0.01.ltoreq.y.ltoreq.0.9), and
includes a Th.sub.2Ni.sub.17 crystal phase or a TbCu.sub.7 crystal
phase as a main phase.
[0028] Similar to the first embodiment, the magnetic material for
magnetic refrigeration of the second embodiment realizes a second
order magnetic phase transition by a material (material having the
rare earth element R in a small amount) which has rare earth
element R and Fe as main components and inexpensive Fe as a base.
The R--Fe based magnetic material exhibits a second order magnetic
phase transition with an inexpensive composition and has a Curie
temperature near room temperature (e.g., Curie temperature of 250K
or more and 320K or less) based on the selection of the element R.
But, there is a possibility that a sufficient magnetic entropy
change amount (.DELTA.S) cannot be obtained when only the R--Fe
based composition is used.
[0029] The magnetic material for magnetic refrigeration of the
second embodiment has the rare earth element R partially replaced
by an element X (at least one of element selected from Ti, Zr and
Hf) having an atomic radius smaller than that of the rare earth
element R. Thus, by replacing the rare earth element R partially by
the element X, the Th.sub.2Ni.sub.17 crystal phase or the
TbCu.sub.7 crystal phase is stabilized. Accordingly, magnetization
is increased, and a large magnetic entropy change amount (.DELTA.S)
can be obtained. In other words, the magnetic material of the
second embodiment is inexpensive and excels in performance and
practical utility, and it is suitably used for the heat
regenerator, the magnetic refrigeration device and the like. At
that time, it can also be used in combination with the magnetic
material exhibiting a first order magnetic phase transition.
[0030] In order to obtain a replacement effect of the element X,
the value y in the formula (2) shall be in a range from 0.01 to
0.9. When the value y is less than 0.01, a stabilization effect of
the Th.sub.2Ni.sub.17 crystal phase or the TbCu.sub.7 crystal phase
by the replacement by the element X cannot be obtained
sufficiently. When the value y exceeds 0.9, it is hard to produce
the Th.sub.2Ni.sub.17 crystal phase and the TbCu.sub.7 crystal
phase. The value y is preferably in a range from 0.01 to 0.5. The
value x shall be in a range from 4 to 20 atomic % in order to
produce the Th.sub.2Ni.sub.17 crystal phase and the TbCu.sub.7
crystal phase. When it deviates from the range, it is hard to
produce the Th.sub.2Ni.sub.17 crystal phase and the TbCu.sub.7
crystal phase. The value x is more preferably in a range from 8 to
15 atomic %.
[0031] The rare earth element R of the second embodiment may be at
least one selected from La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm,
Yb and Y and not limited to a special one. By using Ce, Pr, Nd, Sm
or the like as the rare earth element R, the saturation
magnetization of the magnetic material can be increased. Therefore,
the element R preferably contains at least one selected from Ce,
Pr, Nd and Sm in 50 atomic % or more of a total amount of the
element R. Besides, the element R is more preferably composed of at
least one selected from Ce, Pr, Nd and Sm.
[0032] The magnetic material of the second embodiment is not
limited to the composition expressed by the formula (2) but may
have a composition which has Fe partially replaced by another
element. A part of Fe may be replaced by at least one of element M2
selected from V, Cr, Mn, Co, Ni, Cu, Zn, Nb, Mo, Ta, W, Al, Si, Ga
and Ge. By replacing the Fe partially by the element M2, magnetic
anisotropy, a Curie temperature and the like can be controlled. The
element M2 is more preferably at least one selected from Ni, Co,
Mn, Cr, V, Nb, Mo, Al, Si and Ga. But, if the replacement amount by
the element M2 is too large, magnetization is decreased, and a
magnetic entropy change might be decreased. Therefore, the
replacement amount by the element M2 is preferably 20 atomic % or
less of Fe.
[0033] The magnetic materials for magnetic refrigeration according
to the first and second embodiments are produced as follows. First,
an alloy containing prescribed amounts of individual elements is
produced by an arc melting or an induction melting. For production
of the alloy, a rapid quenching method such as a single roll
method, a double roll method, a rotary disk method or a gas
atomization method, and a method using solid-phase reaction such as
a mechanical alloying method may be applied. The alloy can also be
produced by a hot press, spark plasma sintering or the like of
material metal powder without through a melting process.
[0034] The alloy produced by the above-described method can be used
as a magnetic refrigeration material depending on the composition,
the production process and the like. Besides, the alloy is
annealed, if necessary, so to control the constituent phase (e.g.,
single-phasing of the alloy), to control the crystalline particle
diameter and to improve the magnetic characteristic and then used
as a magnetic refrigeration material. An atmosphere in which
melting, rapid quenching, mechanical alloying and annealing are
performed is preferably an inert atmosphere of Ar or the like in
view of prevention of oxidation. The main phase crystal structure
can be controlled depending on a difference in the production
method and production conditions. For example, in a case where a
magnetic material is produced by the rapid quenching method or the
mechanical alloying method, the TbCu.sub.7 crystal phase tends to
be produced.
[0035] Then, specific examples of the invention and evaluated
results thereof will be described.
EXAMPLES 1 TO 7
[0036] First, high-purity materials were blended at a prescribed
ratio to prepare the compositions shown in Table 1, and mother
alloy ingots were produced by an induction melting in an Ar
atmosphere. The mother alloy ingots were thermally treated in an Ar
atmosphere at 1100.degree. C. for ten days to produce magnetic
materials for magnetic refrigeration. The individual magnetic
materials were examined for appeared phases by X-ray powder
diffraction to find that they had a Th.sub.2Zn.sub.17 crystal phase
or a Th.sub.2Ni.sub.17 crystal phase as a main phase. The main
phases of the individual magnetic materials are shown in Table
1.
EXAMPLES 8 TO 11
[0037] Individual mother alloy ingots having the compositions shown
in Table 1 were produced in the same way as in Examples 1 to 7, and
their mother alloys were partially used to produce quenched thin
ribbons. The quenched thin ribbons were produced by melting the
alloys by induction melting in an Ar gas atmosphere and injecting
the molten alloy onto a rotating copper roll. The roll was
determined to have a peripheral velocity of 30 m/s. The obtained
quenched thin ribbons (magnetic materials for magnetic
refrigeration) were examined for appeared phases by X-ray powder
diffraction to find that they had a Th.sub.2Ni.sub.17 crystal phase
or a TbCu.sub.7 crystal phase as a main phase. The main phases of
the individual magnetic materials are shown in Table 1.
COMPARATIVE EXAMPLES 1 TO 4
[0038] Single Gd (Comparative Example 1), an Sm.sub.2Fe.sub.17
based material (Comparative Example 2), a Ce.sub.2Fe.sub.17 based
material (Comparative Example 3), and an La(Fe, Si).sub.13 based
material (Comparative Example 4) were produced in the same way as
in Examples 1 to 7. The main phases of the individual materials are
shown in Table 1. TABLE-US-00001 TABLE 1 Composition Main phase
Example 1
(Sm.sub.0.3Er.sub.0.1Pr.sub.0.5Ce.sub.0.1).sub.12.2Fe.sub.87.8
Th.sub.2Zn.sub.17 Example 2
(Sm.sub.0.3Pr.sub.0.5La.sub.0.2).sub.11.5Fe.sub.88.5
Th.sub.2Zn.sub.17 Example 3
(Sm.sub.0.4Er.sub.0.1Nd.sub.0.5).sub.12.0(Fe.sub.0.9Ni.sub.0.1).-
sub.88.0 Th.sub.2Zn.sub.17 Example 4
(Sm.sub.0.4Er.sub.0.1Dy.sub.0.5).sub.8.0(Fe.sub.0.9Mn.sub.0.1).s-
ub.92.0 Th.sub.2Ni.sub.17 Example 5
(Sm.sub.0.3Er.sub.0.1Pr.sub.0.5Gd.sub.0.1).sub.15.0Fe.sub.85.0
Th.sub.2Zn.sub.17 Example 6
(Er.sub.0.4Ce.sub.0.2Nd.sub.0.4).sub.12.5Fe.sub.87.5
Th.sub.2Zn.sub.17 Example 7
(Sm.sub.0.5Pr.sub.0.3Tb.sub.0.2).sub.12.0Fe.sub.88.0
Th.sub.2Zn.sub.17 Example 8
(Pr.sub.0.4Sm.sub.0.5Dy.sub.0.1).sub.10.2Fe.sub.89.8 TbCu.sub.7
Example 9 (Pr.sub.0.3Sm.sub.0.5Zr.sub.0.2).sub.9.8Fe.sub.90.2
Th.sub.2Ni.sub.17 Example 10
(Pr.sub.0.3Nd.sub.0.2Zr.sub.0.4Hf.sub.0.1).sub.10.2 TbCu.sub.7
(Fe.sub.0.9Ni.sub.0.05Al.sub.0.05).sub.89.8 Example 11
(Ce.sub.0.2Pr.sub.0.5Zr.sub.0.2Ti.sub.0.1).sub.10.5Fe.sub.89.5
TbCu.sub.7 Comparative Gd Gd Example 1 Comparative
Sm.sub.11.5Fe.sub.88.5 Th.sub.2Ni.sub.17 Example 2 Comparative
Ce.sub.11.5Fe.sub.88.5 Th.sub.2Ni.sub.17 Example 3 Comparative
La.sub.6.7(Fe.sub.0.88Si.sub.0.12).sub.86.6H.sub.6.7 NaZn.sub.13
Example 4
[0039] Then, the individual magnetic materials of Examples 1 to 11
and Comparative Examples 1 to 4 were determined for a magnetic
entropy change amount .DELTA.S(T, .DELTA.H) with an outer magnetic
field varied from magnetization measurement data by using the
following formula. In the formula, T denotes a temperature, H
denotes a magnetic field, and M denotes magnetization.
.DELTA.S(T,.DELTA.H)=.intg.(.differential.M(T,H)/.differential.T).sub.HdH-
(H;0.fwdarw..DELTA.H)
[0040] In any case, the .DELTA.S indicates a peak for arbitrary
.DELTA.H at a prescribed temperature (T.sub.peak). The T.sub.peak
corresponds to a Curie temperature. Table 2 shows temperatures
(T.sub.peak) at which the magnetic entropy change amounts of the
individual magnetic materials exhibit peaks, magnetic entropy
change amounts (.DELTA.S.sub.max (absolute value)) for magnetic
field changes (.DELTA.H=1.0 T) at T.sub.peak, and the temperature
widths (.DELTA.T) satisfying .DELTA.S>.DELTA.S.sub.max/2 on the
.DELTA.S.sub.max-T curve. TABLE-US-00002 TABLE 2 T.sub.peak
|.DELTA.S.sub.max| .DELTA.T (K) (J/kg K) (K) Example 1 315 2.8 30
Example 2 305 2.4 28 Example 3 300 2.6 23 Example 4 298 2.2 30
Example 5 318 2.5 25 Example 6 290 2.4 28 Example 7 310 2.5 24
Example 8 Example 9 295 2.7 26 Example 10 305 2.3 24 Example 11 310
2.5 29 Comparative Example 1 295 3.2 28 Comparative Example 2 375
1.7 25 Comparative Example 3 215 1.5 23 Comparative Example 4 277
16 7
[0041] It is apparent from Table 2 that the individual magnetic
materials of Examples 1 to 11 show .DELTA.S.sub.max and .DELTA.T
equivalent to those of Gd of Comparative Example 1 though a rare
earth element is contained in a small amount. It contributes
greatly to provision of the magnetic material exhibiting a second
order magnetic phase transition at a low cost. Meanwhile, it is
seen that Comparative Example 2 is poor in performance because it
has small .DELTA.S.sub.max though the .DELTA.T shows a good value.
Comparative Example 3 is poor in T.sub.peak, .DELTA.T and
.DELTA.S.sub.max. It is seen that the La(Fe, Si).sub.13 based
material of Comparative Example 4 has a rare earth element in a
small amount and shows large .DELTA.S.sub.max but has a small value
.DELTA.T and drawbacks in a practical view because it uses a first
order magnetic phase transition.
[0042] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *